The present invention relates to an extrusion apparatus and a method for extrusion.
An extrusion apparatus is disclosed, for example, in DE-OS 31 33 708. In an extrusion apparatus of this type, it is intended that the quality of the raw materials in delivery to the extruder be maintained as uniform as possible and in the best possible condition, whereby the material delivery is effected in a radial direction with respect to the extruder worm. There are frequently fluctuations in the performance delivered by such extrusion solutions, in spite of the surplus delivery thereto of the material to be extruded. The noted publication teaches the creation of a special storage or reserve zone which is comprised of a screw element in the extruder housing, whereby an improved and uniform or homogenized distribution of the delivered material should result from this approach.
On the other hand, however, the above-described extrusion solution has not prevailed in that there exists a substantial problem in connection with the radial one-sided loading of the extrusion worm. The delivery of the material effects a substantially strong pressure between the topside of the extruder housing, which is adjacent the delivery funnel, and the extrusion worm. At that location, the material to be worked is compromised and shear loaded with the effect that the extrusion worm is pressed downwardly.
In order to prevent the downward sliding of the extrusion worm on its side onto the extruder housing due to the through bending of the extrusion worm, a predetermined amount of play is typically provided. However, this play on the other hand reduces the working efficiency of the extrusion worm in that the separation thus created leads to the creation of a certain backflow, whereby the to be extruded material in this separation is therein very strongly shear loaded, which is not an especially positive contribution to the properties of the material.
Insofar as the magnitude of the thus produced pressure and the consequent strength of the through bending is a function of the to be extruded material and also the temperature to which the extrusion apparatus has been pre-heated, a certain security reserve must be built into the operation which further reduces the working efficiency.
It is further known to widen an advancement worm in its entry region and at the same time to configure the entry region in a funnel shape. This approach lends itself to the feed of thermoplastic polymeric material granules, whereby the granules are filled into the funnel in a surplus manner and are advanced in the feed direction by the gravity feed of the advancement worm. However, this approach is basically not suited for the feed of elastomeric material in strip form. While granules are already inclined, by virtue of their own weight, to pre-accumulate or thicken, and are therefore suited for feed by pouring, the feed of material prepared in stripsxe2x80x94in other words, generally elastomeric materialxe2x80x94must be performed via special feed rollers as a consequence of which the material is indeed pliable but exhibits a certain basic hardening which detracts from using the material as a flow capable material.
In spite of the known drawbacks, a radial material feed has consistently been used in connection with the feed of elastomeric material as the material to be extruded, and the extruders used in such circumstances most typically have a substantially horizontal extending worm.
The present invention provides a solution to the challenge of providing an extruder which combines an improvement in the extrusion performance with an improved suitability of the to be extruded material strips having various properties.
The solution provided by the present invention is realized by the main claims hereof with additional advantageous features of the invention being set forth in the dependent claims hereof.
In accordance with one embodiment of the extrusion apparatus of the present invention, a substantially axis parallel feed of the to be extruded material is secured by the inventive sleeve or socket. A uniform feed characteristic of the material feed pulse through the inventive inter-peripheral space defined between the socket and the extrusion worm, which tapers in a progressively more restrictive manner, is achieved by the setting of the speed of the extrusion worm and the socket relative to one another. The relative speed difference is a value other than zero but need not be large; instead, it can be discernibly less than the extrusion speed itself. In this manner, the shearing effect of the material is reduced to the required minimum although the desired uniform feed characteristic and, thereby, the filling of the inter-peripheral space is ensured.
The solution of the present invention is particularly advantageous in that, for the first time, an axis parallel feed stocking is made possible notwithstanding the horizontal orientation of the extrusion worm. The extrusion worm is loaded not in a sidewise manner but, instead, only in an axial manner whereby the extrusion worm does not experience any through bending exerted by the material feed pulse. At the same time, however, it is possible to reduce the play between the extruder housing and the extrusion worm so as to thereby improve the working efficiency.
In accordance with the present invention, it is particularly advantageous if the annular gap or inter-peripheral space between the socket and the extrusion worm reduces progressively in size in an axial direction. The material fed to the extruder in strip form can be initially engaged by the extrusion worm or the socket and is then automatically drawn into the conical inter-peripheral space through the spiral-threaded passage of the extrusion worm. However, a thickening results which reduces the possibility that an intake of air occurs, whereby, also, the force introduced due to this circumstance becomes a circumferential force which is applied radially uniformly outwardly against the socket and, on the other hand, radially uniformly inwardly against the extrusion worm and, moreover, the extrusion worm and the extruder housing are loaded in the axial direction. Axial forces can be routinely handled, however, by suitable bearings without additional accommodations beyond that.
In accordance with the present invention, it is particularly advantageous if the socket is provided with an inner thread. The inner thread is preferably configured such that its thread course or path is counter to that of the extrusion worm. Through this configuration, there arises both an inner as well as an outer winding course that supports the feed operation in the intake region. While in known extrusion apparatus a partial back flow, the so-called back disturbance, poses a problem, which is to be countered by special measures such as, for example, the solution disclosed in DE-PS 4 005 400, the control of the rotational speed of the winding socket in accordance with the present invention permits adjustment of the blockage or build up roll. A blockage roll following the beginning of the plasticizing region serves, on the one hand, to promote uniformity of distribution of the feed surpluses but poses, on the other hand, a source of possible disturbances, whereby it is advantageous if one can maintain in a limiting manner the roll size.
In accordance with the present invention, the extrusion apparatus can advantageously be combined with a winding apparatus by which the to be extruded material, which is in a strip configuration in preparation for feeding, is wound about a drive shaft in the feed region, whereby the material strips are already wound in several wraps prior to reaching the winding socket. In one modification of the extruder apparatus of the present invention, it is provided that the decidedly wide material strips are allowed to hang on the drive shaft in a draped manner, whereby the width of the strips in this approach is preferably three-fourths of the circumference of the drive shaft. The winding socket of the present invention can thereupon promote uniform distribution of the material feed about the periphery in that the relative rotation between the winding socket and the extrusion worm ensures that the remaining fourth, which does not have a material strip hanging thereover, is provided with the material advanced in the peripheral direction.
The configuration of the extrusion apparatus involving the hanging material strips permits the use of decidedly thick and thus correspondingly slower to be fed material strips that are at the same time similarly wide. In this manner, the extrusion apparatus of the present invention is also suitable for a high performance classification.
It is to be understood that the rotations per unit time of the inventive winding socket are adaptable across a wide range to the extrusion requirements. It is preferable if the rotational direction of the winding socket is counter to that of the extrusion worm and that the winding socket""s rotations per unit time are as large as or less than the rotations per unit time of the extrusion worm and, consequently, the rotations per unit time of the drive shaft. In a modified configuration of the extrusion apparatus of the present invention, it is provided, to be sure, that the direction of rotation of the winding socket is the same as that of the extrusion worm although the rotation per unit time of the winding socket in this configuration is relatively less than that of the extrusion worm. This configuration also produces relative rotational speed, having a value other than zero, which is of inventive significance. This leads to a uniform distribution of a material feed pulse due to the inter-peripheral distribution.
While it is preferred in accordance with the present invention that the winding course of the socket be disposed in the immediate vicinity of the extruder housing to thereby permit a thermal equilibrium to be reached between the typically heated extruder housing and the socket, it is provided, in another modification of the extrusion apparatus of the present invention, that the winding socket can be spatially uncouplable so as to be disposed in the transition region between the drive shaft and the extrusion worm. By this approach, an axial displacement capability for the winding socket can be decidedly easily ensured, whereby it is, however, preferred that the plasticizing of the to be fed material has already been promoted by at least one indirectly heated winding socket.
The winding socket includes at its intake region an intake taper that is either fixed against rotation relative to the winding socket or is fixed against rotation relative to the extruder housing. The intake taper permits the engagement, as well, of decidedly steeply inclined material strips hanging thereat, for example when the extruder is to be run in an empty or uncharged condition and a cleaning substance is extruded.
The inventive socket can alternatively be provided with an interior frictional surface which effects the desired feed operation counter to the feed operation of the extrusion worm without, however, exerting the size reducing and re-configuring effects on the material as are exerted by feeding of the material via a threaded passage.
In a particularly advantageous configuration of the extrusion apparatus of the present invention, it is provided that several material strips are to be fed in the feed operation. While special measures must be implemented in the use of the extrusion apparatus heretofore known in order to ensure an intensive cross mixing of several material strips, the extrusion apparatus of the present invention permits the degree of cross mixing of the material to be already so increased, at the intake side of the extrusion worm, that the so-called transfer region can be omitted. The cross mixing which already occurs in the region of the inventive socket can be adapted to a wide range of requirements by, on the one hand, the temperature of the socket as well as, on the other hand, the rotation per unit time of the socket in relation to the rotation per unit time of the extrusion worm.
It is therefore possible, for example, to allow the flow of the heating medium through the socket, at least in the area of its housing, which also flows through the extruder housing. Due to the relatively close connection between the socket housing and the actual socket, the socket is brought up to the required temperature. In this manner, the extent over which the heating of the materials is provided is inventively automatically lengthened whereby a uniformity of the heating effect occurs. In accordance with the present invention, a particular pipe effect occurs due to the movement produced on the outer periphery of the material being fed which benefits the degree of cross mixing occurring in the intake region of the extruder. Overall, the inventive socket permits an improved extrusion quality by the intake of various materials as well, whereby it is to be understood that the advantages of the present invention are not limited to the use of elastomeric material.
It is self-evident that the angle at which the material in the feed region is fed in is adaptable to a wide range of requirements. For example, the strip feeder for feeding the material strips can be configured such that its outlet axis extends at an angle of, for example, 30 degrees relative to the shaft, whereby the intersection point of the outlet axis with the shaft can then advantageously lie closely behind the beginning of the shaft xe2x80x94thus, adjacent the associated drive motor. The material strips are then directionally reoriented upon their engagement with the shaft and, in fact, are reoriented along an axial direction so that, at the latest upon the reaching of the transition region between the drive shaft and the extrusion worm, the strips run parallel to the axis of the shaft.
Further advantages, details, and features are set forth in the following description of one exemplary embodiment of the present invention together with the one figure of the drawing.